In cyclocross a hot lap is a practice lap taken at full speed. Before a race hot laps are an all-important step in warming up. After registering, going to the bathroom, checking out the course, going to the bathroom, dressing and eating, going to the bathroom, warming up, and going to the bathroom, hot laps serve as a final check on tire pressure, traction, and chosen line, since everything is different at full speed.
Cyclocross practices are not races. Not even "practice races." Even an informal practice race (Chamois Time in Iowa City, for example) is official enough to count for USAC points and, more important, to require event insurance. For cyclocross practice there is no fee, no registration, and no results. Only fun in a public park. So in cyclocross practice we don't race, we ride hot laps.
Need competition to really rev up your engine? No problem. Hot laps can be one big start, like Renegade Cross, or just rubbing elbows with whoever comes by.
You probably know who you're close to. If not, you will soon. Challenge them to a hot lap. Or two or three. Then repeat.